Estimating distribution, fluctuation and/or movement of electrical activity through a heart tissue

ABSTRACT

A computer implemented method for processing measurement data from electrocardiogram, ECG, electrodes on a subject. The method includes obtaining a 3D anatomical model of the torso of the subject, and obtaining a 3D image of the torso of the subject. The three dimensional image is aligned with the three-dimensional model. A position of each electrode in the three-dimensional model is determined from the three dimensional image. The positions of the electrodes in the three dimensional model are used for estimating the distribution, fluctuation and/or movement of electrical activity through heart tissue.

FIELD OF THE INVENTION

The invention relates to electrocardiogram (ECG) technology. More inparticular the invention relates to generating a model of a heart usingECG measurements. More in particular the invention relates to estimatingthe distribution, fluctuation and/or movement of electrical activitythrough heart tissue. More in particular, the invention relates tolocating heart dysfunction such as locating an origin of prematureventricular contraction (PVC) tachycardia (VT), atrial tachycardia (AT),Wolff-Parkinson-White syndrome (WPW) and conduction orders in a heart onthe basis of ECG measurements.

BACKGROUND

The inventors have to date made progress in so called inversecomputations where e.g. an activation sequence and/or other parametersof the heart are estimated from surface electrocardiograms. Inverseimaging of electrical activity of a heart muscle is for instancedescribed in published patent application US-2012-0157822-A1.

The inventors devised a computer program, herein referred to as CardiacIsochrone Positioning System (CIPS), which using only the standard12-lead ECG quantitatively localizes the origin of PVCs in patients.

SUMMARY

CIPS can use any electrode position on the chest wall: consequentlythere are no misplaced electrodes. However, the exact location of theelectrodes is critical to the outcome of CIPS. Therefore the inventorsdeveloped three-dimensional (3D) Camera software integrated into CIPSthat localizes the ECG electrodes.

The accurate electrode positions are required by the cardiac isochronespositioning system. Therefore a 3D camera based system was developed tolocalize the electrodes.

The 3D camera is used to take 3D images of the torso of subjects withECG electrodes attached. The software transforms the 3D quantitativeimage into a subject specific electrode torso model. These torso modelswere scaled to obtain an objective standard for electrode misplacement.

The 3D camera computer software automatically and rapidly detectsmisplacement of e.g. 12-lead ECGs electrodes.

The invention relates to a computer implemented method for processingmeasurement data from electrocardiogram, ECG, electrodes on a subject.The method includes obtaining a three-dimensional, 3D, anatomical modelof the torso of the subject. Preferably, the anatomical model includesboth an outer surface and positional information on internal structuressuch as the heart and lungs. The three-dimensional anatomical model ofthe torso of the subject can e.g. be derived from a medical imagingmodality, such as MRI, CT, PET-CT, ultrasound, or the like.

The method also includes obtaining a three-dimensional image, such as athree-dimensional photograph, of the torso of the subject includingposition information of the electrodes. The three-dimensional imagecontains a three-dimensional representation of an outer surface of thetorso of the subject. The three-dimensional image also includes positioninformation on the electrodes positioned on the outer surface of thetorso. The three-dimensional image may be obtained using a 3D camera.The three-dimensional image may e.g. be a three-dimensional photographor video recording. The position information of the electrodes may beformed or derived from the electrodes being visible in thethree-dimensional image. The three dimensional image is aligned with thethree-dimensional model. The aligning can include minimizing thedistances between the three-dimensional image and the three-dimensionalmodel.

A position of each electrode in the three-dimensional model isdetermined from the position of each electrode in the overlain threedimensional image. Using the positions of the electrodes in the threedimensional model the distribution, fluctuation and/or movement ofelectrical activity through heart tissue are estimated.

According to an aspect of the invention, a position of each electrode inthe three-dimensional model is determined from the aligned threedimensional image. The positions of the electrodes in the threedimensional model are used for estimating the distribution, fluctuationand/or movement of electrical activity through heart tissue.

A fastest route algorithm, in particular together with a equivalentdouble layer model, allows for so-called inverse functional imaging ofelectrical activity (activation, recovery) of a heart muscle, inparticular of a complete image of a heart, as well as particular areasof interest both on the outside (epicardium) and inside (endocardium) ofthe heart or both. As an algorithm that may lead to comparable resultsas the fastest route algorithm, the fast marching algorithm, theshortest path algorithm, the ion kinetic model or the cellular automatonmodel may be used. This is for instance described in US2012/01257822,incorporated herein by reference.

An ECG is defined herein as any method that (preferably non-invasively)correlates actual electrical activity of the heart muscle to measured orderived (electrical activity) of the heart. In case of a classicalelectrocardiogram the differences in potential between electrodes on thebody surface are correlated to the electrical activity of the heart.Derived ECG's can also be obtained in other ways (e.g. by measurementmade by a so-called ICD (Implantable Cardioverter Defibrillator)). Inorder to obtain such a functional image an estimation of the movement ofthe electrical activity has to be provided.

According to an aspect, the method further includes determining anidentification of each electrode from the three-dimensional image. Theidentification can be one of a color, a shape, or a code. The method canfurther include detecting positions of each a plurality of electrodes,comparing the detected positions with predetermined positions anddetermining whether the electrodes are positioned approximately in thecorrect predetermined position. Thus, it is for instance possible todetermine whether or not the electrodes are positioned in swappedpositions. Electrodes that are supposed to be positioned in an order V1,V2, V3, V4, may, e.g. be actually positioned in an order V1, V4, V3, V2.Once swapped positions have been detected, the program may take theseswapped positions into account. The program may internally swap thesignals received from the swapped electrodes so that the processedsignals correspond to the correct electrode positions. Therefore a needfor repositioning swapped electrodes may be obviated.

According to an aspect, the method includes indicating whether theelectrodes are positioned in a desired position. The electrodes may e.g.be positioned inaccurately. The program may be arranged for indicating adirection and/or distance for repositioning an electrode.

When the underlying anatomy of the patient is known (e.g. from a MRI/CTmodel) the system can also be used to guide lead placement, i.e. makesure the electrodes are over the area of interest. This can be patientspecific. For certain patients, (e.g. Brugada) it is known that thestandard 12 lead ECG electrode positions do not measure the knowndeviations in the ECG. Electrodes need to be put higher in such case.How high can now be related to the cardiac anatomy underneath theelectrodes. This will also help CIPS to improve the diagnosis for thesepatients.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described in detailwith reference to the accompanying drawings.

FIG. 1. Overview of the 4 modules of CIPS: PVC selection (equivalent toSelection of a single atrial or ventricular heart beat from the ECG),CT/MRI derived models, the in this application described new method toregister the electrodes to the torso model derived from MRI/CT.

FIG. 2. Left detection of QRS's (dotted and dashed lines, middle baseline corrected, and selected beat (right).

FIG. 3. The three volume conductor effects: a) proximity effect, b)spatial orientation, and c) volume conduction; bloods conducts betterthan myocardial tissue, lungs worse.

FIG. 4. Rough tuning of the first activation sequence: For each node andnode on the heart an activation sequence is created (left matrix). Fromthese activation sequences the ECG can be computed (Eq 2). Theactivation (node) resulting in the highest correlation between measuredand simulated ECG is taken as the initial estimate.

FIG. 5. Reconstruction of a torso with a 3D camera.

FIG. 6. How the 3D camera works.

FIG. 7. Alignment of 3D image with torso model.

FIG. 8. 3D image as taken with the Kinect camera. Clearly visible arethe electrodes of V1-V4 at the standard positions and one intercostalspace below and above.

FIG. 9. Torso models with electrodes: The standard 12 lead ECG positionsand the three misplaced electrode configurations 1), 2), and 3).

FIG. 10A. the scaled height of the electrodes of the precordial leadswith respect to the reference point of all 5 subjects. In solid linesthe electrodes at the standard positions, in dotted lines electrodeswere shifted one intercostal space up and in dashed lines oneintercostal space lower.

FIG. 10B. Extremity leads shown in the frontal plane. The thick lineindicates the location of the LL electrode in the Mason-Likar position,which can easily be detected.

FIG. 11. Precordial electrodes one intercostal space higher and lower:The standard 12 lead ECG of case 4 (dotted line) one intercostal spacehigher (solid line) and one intercostal space lower (dashed line). Note:the major differences in V1-4 that need to be corrected.

FIG. 12. Misplaced Lead Reconstruction: standard 12 lead ECG of case 5(dotted line), misplaced electrode positions (dashed line), andreconstructed ECG at the standard positions (solid line). Note; V2 andV3 were completely reconstructed whereas V1 was not.

DETAILED DESCRIPTION

CIPS can be used to localize the PVC origin or any other atrial orventricular arrhythmia by electrodes accurately placed in the standard12 lead ECG positions.

In this example the electrodes were moved up and down in 10 mmincrements. For each of these moved electrode positions, CIPS was usedto localize the PVC origins. This change in PVC origin location asdetermined by CIPS was compared to the displacement of the ECGelectrodes. To investigate the registration reproducibility of CIPS, 5images were registered manually to the MRI derived torso model on whichthe electrode positions were projected from the 3D image.

In seven patients, the PVC origin was localized correctly by CIPS to theablation sites with accurately positioned electrodes. However, recordedchanges in PVC origins varied greatly from 0 to 110 produced by 10 mmincrements up to a range of 9-110 mm when moving the electrodes 30 mmdown. The registration error of integrating the 3D image with the MRIderived torso model was less than 2.5 mm per electrode.

Using CIPS, even with a 10 mm change of the electrodes the error forlocalization of PVC are highly variable and large. The CIPS softwarethat integrates and registers the 3D camera image of the electrodes tothe MRI derived torso model is reproducible.

The 3D camera is useful for quantitative localization of electrodepositions for CIPS to accurately localize the origins of the PVCs,ventricular tachycardia (VT), atrial tachycardia (AT),Wolff-Parkinson-White syndrome (WPW), conduction orders and Delta wavesusing the 12 lead ECG in the electrophysiology (EP) Lab and in thegeneral clinical setting. This example highlights the advantage ofrelating the accurate position of the electrodes to the cardiac anatomyas imaged with the 3D camera instead of using the standard position ofthe rib interspaces.

FIG. 1 shows a schematic overview of a system 1 according to theinvention. The system includes a model input unit 2 for obtaining athree-dimensional, 3D, anatomical model of the torso of the subject. InFIG. 1 the 3D model data is obtained from a CT/MRI system 8. The systemfurther includes an image input unit 2 for obtaining a three-dimensionalimage of the torso of the subject. In FIG. 1 the 3D image data isobtained from a 3D camera 10, here a Kinect camera. The system furtherincludes an ECG input unit 2 for obtaining ECG data.

The system in FIG. 1 further includes a processor 4. The processor 4 isarranged for aligning the three dimensional image with thethree-dimensional model, determining a position of each electrode in thethree-dimensional model from the three dimensional image; and using thepositions of the electrodes in the three dimensional model forestimating the distribution, fluctuation and/or movement of electricalactivity through heart tissue.

The process performed by the processor, such as by a computer programrunning on the processor, is described herein below.

Selection of a Single Atrial or Ventricular Heart Beat from the ECG

CIPS analyses single atrial or ventricular complexes. This requires aQRS detection algorithm and a baseline correction procedure. From thesesignals automatically or manually the clinical interesting beats can beselected for analysis (see FIG. 2). This selection is done using a firstmodule. The first module is herein also referred to as selection module.

CT/MRI Derived Models

A second module describes the model creation and the way these modelsare used to compute an ECG on any location on or inside the thorax:

-   -   1) Cardiac current source model linked to cardiac        electrophysiology (Equivalent double layer source model)    -   2) Volume conductor:        -   a. proximity effect, spatial orientation of the 9 ECG            electrodes        -   b. inhomogeneous volume conductor        -   c. Patient's specific geometry from Computed Tomography (CT)            or Magnetic Resonance Imaging (MRI) (FIG. 1),

The first component, the cardiac current source model, is the equivalentdouble layer (EDL). The EDL represents the currents generated by thecardiac tissue during activation and recovery, which is equivalent tothe currents generated by all coupled myocardial cells as recorded atendo- and epicardial surfaces [1], [2]. Consequently, the EDL isreferred to the localization at the endo- and epicardial surface of themyocardium. For any position (node) on the triangulated ventricularsurface, the time course of the local source strength is taken to beproportional to the transmembrane potential (TMP) of the nearby myocytes[3], [4]. The second component accounts for the volume conductoreffects, being: a) proximity and spatial orientation of the 9 ECGelectrodes and b) the differences in conduction properties of thevarious tissues. The proximity effect and spatial orientation isdetermined by the solid angle of the active cardiac tissue as observedfrom the ECG electrodes [5]. The solid angle accounts for the fact thatECG waveforms of electrodes close to the heart are dominated by thecardiac tissue underneath depending on the direction of the wave front.Previous studies indicated that an appropriate volume conductor modelrequires the incorporation of the heart, blood cavities, lungs andthorax [6], [7]. In this example, the conductivity values σ assigned tothe individual compartments were: thorax and ventricular muscle: 0.2S/m, lungs: 0.04 S/m and blood cavities: 0.6 S/m. The mathematicalmethod used to solve this volume conductor problem in a numerical way isreferred to as the Boundary Element Method (BEM) [8], [9]. With the BEMa transfer matrix A can be computed taking into account the fullcomplexity of the discretized volume conductor model. For the potentialsat thorax node l of the 12-lead electrodes is defined by

ECG(t;l)=Σ_(n) A(l,n)S(t;δ _(n),ρ_(n)),  EQ1

in which S(t; δ_(n), ρ_(n)) is the local time dependent EDL sourcestrength, and A(l, n) the BEM derived transfer function relating thecontribution of S at node n to the potentials ECG at thorax node l, orin a matrix notation:

ECG=AS  EQ2

Estimation of Cardiac Activation and Recovery

A fourth module estimates the cardiac activation through a rough- andfine tuning algorithm described in described [10] and in publishedpatent application US-2012-0157822-A1, incorporated herein by reference.Briefly:

-   -   a. The fastest route based initial estimate of cardiac        activation provides the rough initial estimate.    -   b. Optimization procedure is used for the fine-tuning

The fourth module relates to patient-specific geometric models of theheart, lungs and thorax derived from, e.g., Multi Slice ComputerTomography (MSCT) (see FIG. 1).

Previous studies have shown the importance of patient-specific models[11], [12]. These geometric models were created with morphing software[13]. With such software the boundaries of all relevant tissues wereidentified manually. For the ventricles these boundaries are the left-and right endocardium, epicardium, aorta and pulmonary artery. Tocapture the spatial orientation from the 12-lead electrodes, theepicardium and endocardium, lungs, and thorax are morphed to match themanual drawn contour points. This yields a patient specific geometry.

The fourth module uses output from the first and second modules as wellas from a third module described below to, preferably automatically,position the activation isochrones on the endo- and epicardialventricular surface. The rough tuning step is an adapted version of thefastest route to obtain an electrophysiological based initial estimateof the activation sequence as described previously [10], [14]. In short:One ore multiple foci are determined using the fastest route algorithm(see FIG. 3). For each node an activation sequence is computed using aQRS derived propagation velocity. The first estimate of the activationisochrones is the one with the highest correlation between the actualmeasured ECG and the model derived ECG. In the next iteration an extrafocus is added. The activation sequence is computed by the “first come,first served” principle. This procedure is then repeated until there isno increase in correlation found. The final activation isochrones areobtained by a Levenberg-Marquardt based optimization procedure in whichthe rough tuned activation isochrones are tuned to obtain matching ECGs.

The 3^(rd) Module of CIPS: The 3D Camera to Locate and Register theElectrodes Automatically

Localization of the ECG electrodes is important to reduce modelingerrors, i.e. the transfer from the heart surface to the electrodepositions on the chest surface. With a 3D camera, for instance a Kinectcamera, the 3D reconstruction of an object is be created (see FIG. 4).This reconstructed shell of the thorax is be used to create a 3D overlayto the thorax derived from MRI/CT (second module).

As CIPS needs location information of each the electrodes on the chestsurface for every ECG recording it wants to analyze, an algorithm forautomatically determining the location of each electrode is used in thisexample.

Thereto, the system is further provided with a 3D camera. The 3D cameraobtains a 3D image of the torso of a patient. The 3D image of thepatient provides patient specific 3D data of the outer surface of thetorso of the patient. The 3D image contains spatial information in threedimensions on the outer surface of the torso of the patient. Accordingto the invention the patient specific 3D torso data is aligned to a 3Dtorso model of that patient derived from MRI in the EP laboratory. Thisallows for the accurate localization of PVCs by the Cardiac IsochronesPositioning System.

Further, the 3D camera provides location data of the electrodes visiblein the field of view of the 3D camera. The location data includesposition data in three dimensions for each electrode within the field ofview of the 3D camera. Additionally, the 3D camera can be arranged toidentify an identifier of each of the electrodes within the field ofview of the 3D camera. The identifier can e.g. be a color, a shape, anumber, a code or the like. Preferably each electrode has a uniqueidentifier. The identifier of the electrode associated with a certainchannels of the ECG is made known to the system. For instance thechannels/electrodes are color-coded. Thus, the position of eachelectrode can be detected automatically. Currently different color codesare used for the 12 lead ECG system.

Thus, the invention provides for to the automatic alignment of a 3Dimage of the patient torso with the patient specific 3D model of thetorso. The invention also provides for the automatic detection ofelectrode positions on the chest wall.

The 3D image of the torso is automatically aligned to the 3D torso modelderived from MRI/CT using a minimization procedure in which the distancebetween the image points in the 3D image and model points in the torsomodel is reduced automatically. Once aligned, the head of the patientcan be removed automatically to ensure the patient privacy. This mightbe a requirement as photos of the patient are taken. In this example, onthe basis all 3D image data above the shoulders is thereto removed. Asthe position of the shoulders is known from the 3D torso model, thishead removal can be automated in the system.

Next, electrode positions need to be located accurately on the 3D modelof the torso. In this example colored electrodes are used. The electrodepositions can then be automatically detected using the color as anidentifying marker. Other identifying markers like text etc., can beused as well. In the absence of electrode identifiers, the program candetermine the electrode positioned closest to a predefined (e.g.optimum) electrode location, define this electrode as coupled to thatpredefined location, and determine the actual location of that electrodeon the basis of the 3D image.

Notice that for every ECG recording a 3D image is required, aselectrodes can be place anywhere on the chest wall.

The ECG based Cardiac Isochrones Positioning System (CIPS) for exampleuses nine electrodes. The electrode positions on the torso aredetermined to estimating the distribution, fluctuation and/or movementof electrical activity through heart tissue, e.g. to localize accuratelythe origin of the PVC, VT, AT and delta waves [15]. However, in the EPlab the electrodes are frequently not placed in the predeterminedpositions. An example of such predetermined positions are the standardtwelve lead ECG positions. Placing the electrodes in other positionsthan the predetermined positions can be due to other attached system'spatches. The system includes a 3D camera and 3D camera software thatautomatically detects electrode misplacement. Optionally the program isfurther arranged to correct for such misplacements. The 3D quantitativeimage data is used to construct a subject specific torso geometry. To beable to compare electrode misplacement among subjects, in this examplethe torso models were scaled to a standard height, assuming the ribcagescales linearly with torso height. The triangulated torso geometry wasadditionally used to correct the ECG signals from the misplacedelectrodes.

Example

In this example software is used using the Microsoft Kinect softwaredevelopment kit (SDK) version 1.7. However, it will be appreciated thatother 3D cameras and software kits can be used. This software retrievesthe data from the Kinect camera [16] and processes the data to obtainthe subject specific torso models.

Measurement Setup

To test the ability to detect electrode misplacement from 3D imagederived torso models, five subjects were included in this example study.On each subject the 12 lead electrodes were positioned accurately by anexperienced technician. Additionally the precordial electrodes werepositioned one intercostal space higher and one intercostal space lower(see FIG. 8). Extremity electrode positions were unaltered during theECG recording. For each configuration the ECG was recorded while thesubject maintained a supine position.

In FIG. 8 is the 3D image of a subject recorded in the Antero-posteriorposition with the attached electrodes. Therefore the accuracy of the V5and V6 electrodes could not be determined.

Torso Model Construction to Detect Electrode Misplacement

In order to make a 3D computer model, in this example triangles are usedto describe the surface of the human torso. To detect the misplacementof the electrodes a common reference point must be created. Thisrequires the definition of a reference point. For the reference modelthe z-coordinate of the reference point was defined at a quarter of theheight of the torso model (FIG. 10B). The height of the torso was takenas the distance between the shoulders and the crotch. The center of thehorizontal plane at the middle of the torso resulted in the x-coordinateand y-coordinate of the reference point. All subsequent torso modelswere scaled to match the height of the common reference model. Thedistance in the z direction with respect to the reference point was usedto detect the misplacement of leads.

Method for ECG Lead Correction

Three common electrode misplacements configurations were used toreconstruct the ECG signals at the standard positions:

1) V1,2 higher, V3 standard, and V4-6 lower

2) V1,2 and V6 standard, and V3-5 higher

3) V1-3 higher, and V4-6 standard

The ECGs recorded at these misplaced electrode positions were used toreconstruct the ECGs at the standard positions with a surface laplacianbased interpolation method [17].

The differences between reconstructed and recorded 12 lead ECG data werequantified using the relative difference (rd) measure: the root meansquare value of all matrix elements involved relative to those of therecorded ECG data.

Results

As seen in table 1, the KINECT torso models derived chest circumferenceshad a close calibration to the measured chest circumferences. Thedistance between the standard electrodes and the electrodes placed oneintercostal space above was 43±3.5 mm and 42±3.5 mm for the electrodesbelow.

TABLE 1 Calibration of the 3D camera measurement: The chestcircumference directly measured was compared with the 3D camerameasurements. The circumference was measured at the height of 4thintercostal space and from the reconstructed torso model atapproximately the same height. Note their similarity. age Chestcircumference (cm) height subject (years) measured 3D camera (cm) KP00165 108 110 188 KP002 54 107 110 186 KP003 21 87 91 173 KP004 41 84 91177 KP005 42 85 90 192

As shown in FIG. 10A, the electrodes placed one intercostal space aboveor below were calculated by the program to be significantly misplacedusing the distance from leads V1-V6 to the reference point (P≦0.01).

The standard 12 lead ECGs were reconstructed from the three differentmisplaced lead configurations (FIG. 9). In table 2 the relativedifferences (rd) are listed for all subjects and the 3 different leadconfigurations. In five cases the rd increases, in all other cases therd did improve. Only in 4 cases the rd was below 0.2, a value thatcorresponds to a correlation coefficient of more than 98%. Especiallyfor lead configuration 1 the interpolation failed to reconstruct thestandard 12 lead ECG accurately. An example of the reconstruction of theECG at the standard positions from the third misplaced leadconfiguration is shown in FIG. 4. As shown in FIG. 5 the misplaced leadsV2 and V3 are corrected by interpolation but not in V1.

TABLE 2 Correction of misplaced electrode ECGs: Relative difference (rd)before and after correction of the ECG signals. See FIG. 2 for the usedlead misplacement configurations. A rd of 0.2 corresponds to acorrelation coefficient of more than 98%. 1 2 3 before after beforeafter before After KP001 0.37 0.44 0.22 0.20 0.28 0.47 KP002 0.24 0.270.34 0.34 0.21 0.26 KP003 0.23 0.26 0.20 0.09 0.24 0.19 KP004 0.23 0.270.20 0.13 0.24 0.22 KP005 0.41 0.26 0.39 0.24 0.36 0.15

The 3D camera proves to be an appropriate tool to obtain the torsogeometry including the electrode positions on the chest wall. Thus thistool enables the patient specific torso reconstruction in the EPlaboratory, a requirement for the accurate localization of PVCs by theCardiac Isochrones Positioning System [15].

It is possible to detect electrode misplacement by using the visualinformation recorded by a 3D camera. The precordial electrodes locatedapproximately 4 cm from the standard positions could be significantlyclassified as misplaced (FIG. 10). When using a database containing rddata the sensitivity and specificity of distances and angles misplacedleads can be determined accurately, and corrected position informationfor the misplaced leads can be estimated accurately.

In this example, the major underlying assumption in the Torso Model isthat the height of the ribcage, and consequently the standard precordialelectrode positions scales linearly with the torso length. Thisassumption is adequate to detect the electrode misplacement.Furthermore, other landmarks of the torso, such as the angle of Louis orthe xyphoid, might be mathematically derived from these models as well.

Correct electrode placement of the 12 lead ECG is critical for correctcomputerized ECG diagnoses systems. The likelihood of misplacement canbe incorporated in computerized ECG analysis algorithms, thus increasingthe sensitivity and specificity of the applied ECG diagnosis algorithms.As shown in FIG. 10B, the detection of the left leg (LL) electrode inthe Mason-Likar position between the mid-left lower ribcage and theiliac crest.

This position can be converted by the program to the standard positionon the left leg. This lead misplacement algorithm can also be applied inambulances with equipment that transmit the acquired ECG's digitally toa hospital for on-line consulting and diagnosis.

In a significant percentage of the patients suffering from acutecoronary syndrome the diagnosis based on the transmitted ECG's isincorrect [18]. This might result in the transportation of thesepatients to a hospital where a percutaneous coronary intervention (PCI)procedure cannot be performed. Using the 3D camera to detect electrodemisplacement and the use of the program to correct the diagnosis couldreduce the number of patients transported to the wrong facility.

As an experiment, the geometrical information of the torso was used tocorrect the standard 12 lead ECG from the recorded misplaced ECGsignals. In FIG. 11 is demonstrated the leads that need to be correctedare V1-4. In FIG. 12 is shown that the correction method proposed byOostendorp et al. [17] corrected V2-3, but not V1. As shown in Table 2the electrode configuration with V1,2 too high, V3 standard, and V4-6too low produced a reduced match for four out of the five subjects. Thenew technique presented herein has created a new tool to improve thediagnostic accuracy of the standard 12 lead ECG.

New 3D camera computer software can automatically and rapidly detectmisplacement of 12-lead ECGs recording in the EP lab and other locationsand thereby increase the accuracy of the 12 lead ECG. The computerprogram is capable of correcting position information of most of thesemisplaced leads. This correction improves the results obtained from adiagnostic computerized ECG program.

Although the embodiments of the invention described with reference tothe drawings comprise computer apparatus and processes performed incomputer apparatus, the invention also extends to computer programs,particularly computer programs on or in a carrier, adapted for puttingthe invention into practice. The program may be in the form of source orobject code or in any other form suitable for use in the implementationof the processes according to the invention. The carrier may be anyentity or device capable of carrying the program.

For example, the carrier may comprise a storage medium, such as a ROM,for example a CD ROM or a semiconductor ROM, or a magnetic recordingmedium, for example a floppy disc or hard disk. Further, the carrier maybe a transmissible carrier such as an electrical or optical signal whichmay be conveyed via electrical or optical cable or by radio or othermeans, e.g. via the internet or cloud.

When a program is embodied in a signal which may be conveyed directly bya cable or other device or means, the carrier may be constituted by suchcable or other device or means. Alternatively, the carrier may be anintegrated circuit in which the program is embedded, the integratedcircuit being adapted for performing, or for use in the performance of,the relevant processes.

However, other modifications, variations, and alternatives are alsopossible. The specifications, drawings and examples are, accordingly, tobe regarded in an illustrative sense rather than in a restrictive sense.

For the purpose of clarity and a concise description features aredescribed herein as part of the same or separate embodiments, however,it will be appreciated that the scope of the invention may includeembodiments having combinations of all or some of the featuresdescribed.

In the claims, any reference signs placed between parentheses shall notbe construed as limiting the claim. The word ‘comprising’ does notexclude the presence of other features or steps than those listed in aclaim. Furthermore, the words ‘a’ and ‘an’ shall not be construed aslimited to ‘only one’, but instead are used to mean ‘at least one’, anddo not exclude a plurality. The mere fact that certain measures arerecited in mutually different claims does not indicate that acombination of these measures cannot be used to an advantage.

REFERENCES

The following references are referred to above, and incorporated hereinby reference.

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What is claimed is:
 1. A computer implemented method for processingmeasurement data from electrocardiogram, ECG, electrodes on a subjectincluding the computer: obtaining a three-dimensional, 3D, anatomicalmodel of the torso of the subject; obtaining a three-dimensional imageof the torso of the subject including position information of theelectrodes; aligning the three dimensional image with thethree-dimensional model; determining a position of each electrode in thethree-dimensional model from the three dimensional image; and using thepositions of the electrodes in the three dimensional model forestimating the distribution, fluctuation and/or movement of electricalactivity through heart tissue.
 2. The method of claim 1, wherein thethree-dimensional image is obtained with a 3D camera.
 3. The method ofclaim 1, wherein three-dimensional model of the torso of the subject isderived from a medical imaging system, such as MRI, CT, PET-CT,ultrasound, or the like.
 4. The method of claim 1, wherein the aligningincludes minimizing the distances between the three-dimensional imageand the three-dimensional model.
 5. The method of claim 1, furtherincluding determining an identification of each electrode from thethree-dimensional image.
 6. The method of claim 5, wherein theidentification is one of a color, a shape, number, or a code.
 7. Themethod of claim 1, further including detecting positions of each of aplurality of electrodes, comparing the detected electrode positions withpredetermined electrode positions and determining whether the electrodesare positioned approximately in the correct predetermined position. 8.The method of claim 7, further including determining whether electrodesare positioned in swapped positions.
 9. The method of claim 8, furtherincluding swapping back signals of swapped electrodes.
 10. The method ofclaim 1, including indicating whether the electrodes are positioned in adesired position.
 11. The method of claim 10, further includingindicating a direction and/or distance for repositioning an electrode tothe desired position.
 12. The method of claim 1, further includingremoving image data relating to a face of the subject from thethree-dimensional image.
 13. A system for processing measurement datafrom electrocardiogram, ECG, electrodes on a subject, the systemincluding: a model input unit for obtaining a three-dimensional, 3D,anatomical model of the torso of the subject; an image input unit forobtaining a three-dimensional image of the torso of the subject; aprocessor arranged for aligning the three dimensional image with thethree-dimensional model; determining a position of each electrode in thethree-dimensional model from the three dimensional image; and using thepositions of the electrodes in the three dimensional model forestimating the distribution, fluctuation and/or movement of electricalactivity through heart tissue.
 14. The system of claim 13, furtherincluding a 3D camera for providing the three-dimensional image.
 15. Thesystem of claim 13 further including display means for displayingelectrode positions in relating to the three-dimensional image and/orthree-dimensional model.
 16. Non-transitory computer readable mediumstoring computer implementable instructions which when implemented by aprogrammable computer cause the computer to process a three-dimensional,3D, anatomical model of the torso of the subject; process athree-dimensional image of the torso of the subject; align the threedimensional image with the three-dimensional model; determine a positionof each electrode in the three-dimensional model from the threedimensional image; and use the positions of the electrodes in the threedimensional model for estimating the distribution, fluctuation and/ormovement of electrical activity through heart tissue.